1. Field of the Invention
The present invention relates to compensators for laser systems. More specifically, the present invention relates to thermal birefringence compensators for laser rods employed in double pass laser systems.
2. Description of the Related Art
Correcting the thermal birefringence of a laser rod, upon a double pass of the rod, has been accomplished using a 45.degree. Faraday rotator. However, use of a Faraday rotator has a number of disadvantages. First, Faraday rotators are large and expensive devices. Second, Faraday rotators often absorb at the operating wavelength of a laser amplifier. Third, Faraday rotators are easily damaged. Moreover, while Faraday rotators work fine at correcting a rod's thermal birefringence in a double pass amplifier, these rotators are difficult to implement in an oscillator.
In a polarization outcoupled (POC) laser oscillator, two Faraday rotators are necessary, one to correct the rod birefringence and the other to control the outcoupling fraction, which would be 100% otherwise.
Other inventions by this Applicant also assigned to Raytheon Company include:
"Reeder Rotator" (Ser. No. 09/483,254; Attorney Docket No. PD-R98093); "Reeder Rod" (Ser. No. 09/482,230; Attorney Docket No. PD-R98094); and "Waveplate Polarization Rotator" (Ser. No. 09/482,378; Attorney Docket No. PD-R98109). These applications are incorporated herein by reference.
What is needed is an optical device that corrects the thermal birefringence of a laser rod, upon a double pass of the rod. It would be beneficial if the postulated optical device were made entirely of reciprocal optics, i.e., waveplates and prisms. Moreover, it would be desirable if the postulated optical device advantageously could be used in both conventionally and polarization outcoupled oscillators and double pass amplifiers.